As previously reported [6], [30], SOD concentrations were particularly low in severe asthma subjects, blunting the difference between ETS-exposure and non-ETS exposure in this group; and ETS exposure therefore had the most noticeable impact on SOD activity in non-severe asthmatics (SOD activity U/ml serum in non-severe asthma: non-ETS (n = 186), 17.7±0.9, ETS (n = 82), 14.8±1.0, p = 0.02). This evidence concerns the gene SOD1 and asthma.